Diffusion-Coupled Degradation of Chlorinated Ethenes in Sandstone: An Intact Core Microcosm Study

Area of Science:

• Environmental Science
• Geochemistry
• Hydrogeology

Background:

• Chlorinated ethenes are common groundwater contaminants.
• Matrix diffusion is a key process in fractured porous media.
• Understanding contaminant transport and degradation in situ is vital for effective remediation.

Purpose of the Study:

• To investigate diffusion-coupled degradation of trichloroethene (TCE) in a simulated fracture-matrix system.
• To compare degradation in intact cores versus crushed-rock microcosms.
• To evaluate the impact of biostimulation on contaminant transformation.

Main Methods:

• Intact sandstone cores from a TCE-contaminated site were used in diffusion-transport microcosms.
• Simulated fracture flow via advection in a top chamber.
• Biostimulation with lactate was applied.
• Comparison with crushed-rock batch microcosms.

Main Results:

• Lactate stimulated reductive dechlorination of TCE to cis-1,2-dichloroethene (cDCE) in intact cores.
• Higher removal rates of TCE to cDCE observed due to concentration gradients, lower sorption, and higher diffusion coefficient.
• Absence of cDCE to vinyl chloride/ethene reduction in intact cores, suggesting no Dehalococcoides.
• Evidence of abiotic transformation (acetylene formation, stable isotope enrichment).

Conclusions:

• Core microcosms provide a realistic model for chlorinated ethene behavior in fractured rock aquifers.
• Matrix diffusion and fracture flow significantly influence contaminant transport and transformation.
• Biostimulation can enhance TCE degradation, but complete dechlorination may be limited in intact cores.